The [http://www.calcwatch.com/history.htm history of the uWatch] mentions the 53mm x 20mm compact 16x2 line LCD that convinced David L. Jones that the uWatch project was actually doable with off-the-shelf components.

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If you are doing low-level programming of the uWatch, such as making "custom characters", you might want to look at [http://www.electusdistribution.com.au/products_uploaded/QP-5519-2.pdf the datasheet] (via [http://www.calcwatch.com/forum/viewtopic.php?id=37 "Moon Phases"]).

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Alas, that original display pulls about 2 mA, more power than anything else on the uWatch -- even the CPU uses less power (at 250 KHz). That's the main reason the current uWatch cannot [http://www.calcwatch.com/forum/viewtopic.php?id=42 run the display continuously] (like a standard watch), but much be explicitly "turned on" every time you want to read the time.

* [http://www.crystalfontz.com/product/CFAX12864T1WFH.html CFAX12864T1-WFH Graphic LCD]: 128x64 display with EL backlight. Power: 3.3 V at 0.18 mA typical; (the EL backlight version seems to require less power than the [http://www.crystalfontz.com/product/CFAX12864T1TFH.html white LED backlight version]; but how much power is that exactly?).

* [http://www.avesodisplays.com/products/index.html card display]: 6 digit, 7 segment display module designed to fit inside a credit card. lightest-weight display of those on this list; adequate for 4-function calculator watch. Doesn't seem to show enough information for a scientific calculator.

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* [http://www.sparkfun.com/commerce/categories.php?c=76 Sparkfun LCD displays]: the color graphics LCD cell phone displays look relatively low power and are extremely well documented -- some of them are under $20.

Revision as of 14:12, 6 December 2015

Contents

µWatch unofficial FAQs

The uWatch is an RPN and Algebraic scientific calculator watch that you can build yourself.
The software is open source under the GPL license at Sourceforge.
I'm assuming you've already read the official uWatch FAQ, so we'll jump right into some more technical details.

OSWatch

display

The display is perhaps the most critical part of a wrist computer such as the uWatch and the Open Source Watch.

The history of the uWatch mentions the 53mm x 20mm compact 16x2 line LCD that convinced David L. Jones that the uWatch project was actually doable with off-the-shelf components.
If you are doing low-level programming of the uWatch, such as making "custom characters", you might want to look at the datasheet (via "Moon Phases").

Alas, that original display pulls about 2 mA, more power than anything else on the uWatch -- even the CPU uses less power (at 250 KHz). That's the main reason the current uWatch cannot run the display continuously (like a standard watch), but much be explicitly "turned on" every time you want to read the time.

The current uWatch2 rough draft seems likely to use the
Newhaven NHD-C12832A1Z-FSW-FBW-3V3 128x32 Pixels display.
Which uses less than 100uA which would enable a continuous display watch. The "white LED backlight" uses 30 mA at 3.0 V but is still very usable at much lower currents.

Proposed displays:
Limited to less than 10 mW of power when updating the time once a second (FIXME: reduce this limit and prune higher-power displays when this list gets too long):
In no particular order:

card display: 6 digit, 7 segment display module designed to fit inside a credit card. lightest-weight display of those on this list; adequate for 4-function calculator watch. Doesn't seem to show enough information for a scientific calculator.

Sparkfun LCD displays: the color graphics LCD cell phone displays look relatively low power and are extremely well documented -- some of them are under $20.

buttons

The buttons are crucial for a calculator watch.
It is difficult to compromise between:

fast typing speed:

it's much faster to have lots of buttons, so you can directly push a button for "tan" than to scroll through some soft menu searching for it.

large buttons are generally faster to rapidly punch than tiny, closely-packed buttons

physical size:

We want something that is not too heavy and bulky to wear on the wrist. This means lots of large buttons are not going to happen.

The first uWatch prototype used surface-mount buttons.
The original uWatch for sale uses the (through hole!) Panasonic EVQ-PJG05Q switch for its buttons.
[3]
(current price)

please tell us about other buttons that would be appropriate

... capacitive touch "buttons" ? ...

...

processor

The processor is, perhaps surprisingly, not a crucial choice.
In the last few years, several companies have released processors that meet the stringent low-power and other requirements (which are????).
In theory, since most of the software is written in the C programming language, it is theoretically easy to port the software to a different CPU.

The original uWatch uses the 16 bit Microchip PIC24FJ64GA004.
It uses 50uA at 32KHz, ... (FIXME)... uA at 250 KHz.